Arrangement and method for detecting a fatigue fracture of a bolted connection caused by overstressing

Abstract

An arrangement for detecting a fatigue fracture caused by overstressing of a bolted connection including a bolt and an internal-thread-bearing hollow section which is alternately stressed by an axial flux of force between zero and different maximal values. A transverse crack forms at a predetermined breaking point of the bolted connection, at which the hollow section breaks due to fatigue. The spacing of the predetermined breaking point from the connection ends, and the interaction of the bolt and the hollow section, are designed such that, after the breakage, the bolt forms in the hollow section a residual joining connection which can be alternatingly stressed. In order to signal the occurrence of a crack on the hollow section of the bolted connection in the event of a fracture caused by fatigue in a simple and always noticeable manner, the arrangement has an additional signaling device. The signaling device is arranged at least on the section of the residual joining connection formed by the area with play of the bolted connection such that the crack causes its destruction, whereby the device causes at least one signal which can be noticed visually or acoustically. The signaling device may be microcapsules containing dye arranged in the threads, a hollow space adjacent the bolt filled with pressurized gas, or a ripping wire attached to the hollow section.

What is claimed is: 
     
       1. An arrangement for detecting a fatigue fracture due to alternate axial stress in a bolted connection, comprising: a hollow section having an internal thread;   a bolt with an external thread being threaded into said internal thread of said hollow section over an axial distance,   said axial distance including a rearward area extending from a connection end of the bolt with play between said internal thread and said external thread, and a forward area adjacent to said rearward area without play between said internal thread and said external thread,   said rearward area and said forward area defining a predetermined breaking point therebetween at which said hollow section will crack in a transverse direction due to fatigue from said alternate axial stress, said predetermined breaking point being located such that the bolt continues to support the hollow section at the rearward area after said hollow section cracks; and   a signaling device arranged adjacent said predetermined breaking point, said signaling device triggering at least one signal which can be noticed visually or acoustically when said hollow section cracks.   
     
     
       2. An arrangement according to claim 1, wherein said signaling device comprises microcapsules embedded between the internal thread and the external thread along at least a portion of said rearward area, said microcapsules containing a fluidic dye, said microcapsules being crushed when said hollow section cracks such that said dye emerges from the microcapsules and flows through said crack to an exterior side of the hollow section to visually signal said crack. 
     
     
       3. An arrangement according to claim 1, wherein said signaling device comprises a hollow space filled with a pressurized gas and connected with said rearward area, and a pressure cell which is in contact with the hollow space and which emits at least one voltage signal which generates a sound or light signal due to a pressure drop in said hollow space when said hollow section cracks. 
     
     
       4. An arrangement according to claim 1, wherein said signaling device is a ripping wire which is integrated in an electric circuit and which is mounted on an exterior side of the hollow section to span said predetermined breaking point, the ripping wire ripping when said hollow section cracks and triggering an acoustic or visual signal in a consuming device connected with the electric circuit. 
     
     
       5. An arrangement according to claim 4, wherein said consuming device is connected with the electric circuit via a resistance measuring device. 
     
     
       6. A method for detecting a fatigue fracture due to alternate axial stress in a bolted connection comprising a hollow section having an internal thread, a bolt with an external thread being threaded into said internal thread of said hollow section over an axial distance, said axial distance including a rearward area extending from a connection end of the bolt with play between said internal thread and said external thread, and a forward area adjacent to said rearward area without play between said internal thread and said external thread, said rearward area and said forward area defining a predetermined breaking point therebetween at which said hollow section will crack in a transverse direction due to fatigue from said alternate axial stress, said predetermined breaking point being located such that the bolt continues to support the hollow section at the rearward area after said hollow section cracks, said method comprising: arranging a signaling device adjacent said predetermined breaking point, said signaling device triggering at least one signal which can be noticed visually or acoustically when said hollow section cracks.   
     
     
       7. A method according to claim 6, wherein said signaling device comprises microcapsules embedded between the internal thread and the external thread along at least a portion of said rearward area, said microcapsules containing a fluidic dye, said microcapsules being crushed when said hollow section cracks such that said dye emerges from the microcapsules and flows through said crack to an exterior side of the hollow section to visually signal said crack. 
     
     
       8. A method according to claim 6, wherein said signaling device comprises a hollow space filled with a pressurized gas and connected with said rearward area, and a pressure cell which is in contact with the hollow space and which emits at least one voltage signal which generates a sound or light signal due to a pressure drop in said hollow space when said hollow section cracks. 
     
     
       9. A method according to claim 6, wherein said signaling device is a ripping wire which is integrated in an electric circuit and which is mounted on an exterior side of the hollow section to span said predetermined breaking point, the ripping wire ripping when said hollow section cracks and triggering an acoustic or visual signal in a consuming device connected with the electric circuit. 
     
     
       10. An arrangement according to claim 9, wherein said consuming device is connected with the electric circuit via a resistance measuring device.